Apparatus for Spring Centered Caster Wheel

ABSTRACT

An autonomous delivery vehicle having one or more caster wheels that may be held off the ground for a portion of the time that the autonomous delivery vehicle travels. Each caster wheel is mounted in a pivot with a centering mechanism to hold the caster wheels in a design orientation. The caster wheel in the design orientation maximizes the view of forward-looking sensors on the autonomous delivery vehicle. The centering mechanism uses a compression spring that drives a follower and swashshaft to apply a rotation force on the caster wheels. The rotational force urges the casters frame and wheels to return to a design position. The rotational force increases with the rotational difference between the caster rotational position and the design position.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a Divisional Application of Non-ProvisionalU.S. patent application Ser. No. 17/005,408, filed Aug. 28, 2020, andentitled Apparatus for Spring Centered Caster Wheel (Attorney Docket No.AA360), which claims priority from U.S. Provisional Patent ApplicationSer. No. 62/893,267, filed Aug. 29, 2019 and entitled Apparatus forSpring Caster Wheel (Attorney Docket No. AA056), which is herebyincorporated herein by reference in its entirety.

BACKGROUND

The present teachings relate generally to autonomous delivery vehicles,and more specifically to the control of the casters wheels not incontact with the ground. Autonomous Delivery Vehicles (ADV) may securelydeliver one or more packages or items to a desired location. The ADVneeds to orient itself within its environment and navigate the streets,sidewalks, and open spaces to reach a desired destination. In addition,the ADV needs to identify and avoid obstacles and recognize changes intravel surface. Obstacle and/or surface detection relies on short rangesensors include stereo-cameras, short-range radar, ultra-sonic etc.These short range sensors typically observe the area or volume aroundthe ADV out to several meters. In order to improve obstacle/surfacedetection, the movement of ADV components within the field of view ofthe short-range sensors should be limited. Swivel casters rotate orpivot about an axis approximately perpendicular to the wheel axis. Thepivoting of the swivel casters allows the caster wheel contacting theground to align with the direction of travel. In cases, where the swivelcaster is lifted off the ground, the caster may pivot freely and movewithin the FOV of the front and corner short-range sensors. There is aneed for an apparatus to encourage the swivel casters to hold a desiredorientation relative to the ADV.

SUMMARY

Briefly, and in general terms, the present disclosure relates to anapparatus to controlling the rotational position of a caster on avehicle. The apparatus consists of a first part mounted to a base of thevehicle, a second part rotatably mounted within the first part and aspring actuator that acts on the first and second parts. The second partrotates about a castor pivot axis is characterized by its rotationalposition with respect to the first part. The second part has a designrotational position with respect to the first part. The spring actuatorthat applies a force on the second part that increases with an angulardifference between the rotational position and the design position ofthe second part.

The spring actuator includes a compression spring oriented along thecastor pivot axis, a swashshaft attached to the second part and afollower to contacts the spring and the swashshaft. The swashshaftincludes a bearing surface characterized by swashshaft axis thatintersects the caster pivot axis at an acute angle and the bearingsurface is centered on the swashshaft axis. The follower is driven bythe swashshaft and progressively compresses the compression spring asthe anglar difference increases. In an embodiment the follower isrotatably connected to the first part via a pin that is perpendicular tothe castor pivot axis. In another embodiment, the follower is allowed tomove axially and is constrained by the first part from rotating aboutthe caster pivot axis. The follower has a first surface, surface incontact with the bearing surface, so that the first surface isperpendicular to the swashshaft axis when the second part is in thedesign position.

In some embodiments, the second part includes a kingpin, which iskingpin rigidly attached to the swashshaft. The design position alignsthe caster frame with a centerline of the vehicle base.

In some embodiments, the swashshaft includes a fixed portion attached tothe second part and a bearing portion that includes the bearing surface.The bearing portion may be a roller element bearing with an outer race.The outer race may be the only part of the swashshaft that contacts thefollower. The second part may include a caster fork and a caster wheel,where the caster wheel is rotatably attached to the caster fork. Thesecond part may be capable of rotating fully around the caster pivotaxis. The compression spring may be a coil spring, a flat spring or abulk material spring.

Some embodiments of this disclosure may include an autonomous vehicle(AV) that navigates one or more surfaces. The AV includes a containerbase with a controller, a camera having a field of view and a power baseconfigured to move the container base across the one or more surfaces.The power base includes a base structure including a second controller,two clusters disposed laterally on each side of a base and connected tothe base. Each cluster has a front wheel and a back wheel. The powerbase also includes two casters, each caster connected a caster arm witha caster mount, and the the caster arms mounted to each side of thebase. The casters are disposed partially within the camera's field ofview. The caster mount comprise a centering device that urges thecasters to a predetermined orientation when the casters are not incontact with the one or more surfaces.

In some embodiments, the centering device includes a first part mountedto the caster arm, a second part rotatably mounted within the first partand a spring actuator configured to apply a force on the second part.The second part rotates about a castor pivot axis and has a rotationalposition and a design position with respect to the first part. Thespring actuator applies a force on the second part that increases withthe angular difference between a rotational position and the designposition. The spring actuator includes a compression spring orientedalong the castor pivot axis, a swashshaft rigidly attached to the secondpart and a follower. The swashshaft has a bearing surface defined inpart by a swashshaft axis that intersects the caster pivot axis at anacute angle, the bearing surface being centered on the swashshaft axis.The follower contacts the bearing surface and the compression spring.The follower is driven by the swashshaft and progressively compress thecompression spring as the angular difference increases.

In one embodiment of the AD, the follower is rotatably connected to thefirst part via a pin, the pin being perpendicular to the castor pivotaxis. In another embodiment of the AD, the follower is allowed to moveaxially and constrained from rotating about the caster pivot axis.

In some embodiments of the AD, the second part includes a kingpinrigidly attached to the swashshaft.

In some embodiments of the AD the swashshaft includes a fixed portionattached to the second part and a bearing portion that includes thebearing surface. The bearing portion may be a roller element bearingwith an outer race.

BRIEF DESCRIPTION OF THE DRAWINGS

The present teachings will be more readily understood by reference tothe following description, taken with the accompanying drawings, inwhich:

FIG. 1 is an isometric view of the lower portion of an autonomousdelivery vehicle (ADV).

FIGS. 2A-2D are isometric views of the ADV power base.

FIGS. 3A-3B are front views of the ADV lower portion.

FIG. 4 is a side view of a caster assembly.

FIG. 5 is an isometric view of a caster assembly.

FIGS. 6A, 6B are views of the actuator components.

FIGS. 7A-7B are isometric views of the follower

FIGS. 8A-8B are isometric views of the swashshaft.

FIGS. 9A-9B are views of the caster assembly

FIGS. 10A-10C are views of the caster assembly with an alternativefollower.

DETAILED DESCRIPTION

The autonomous delivery vehicle (ADV) 100 in FIG. 1 may deliver cargoand/or perform other functions involving autonomously navigating to adesired location. In some applications, the ADV 100 of FIG. 1 may beremotely guided. A cargo container (not shown) is mounted on the cargoplatform 160, which is mechanically connected to the power base 170. Thepower base 170 includes four powered wheels 174 and two caster wheels176. The power base 170 provides speed and directional control to movethe ADV 100 along the ground and over obstacles including curbs andother discontinuous surface features.

The cargo platform 160 is connected to the power base 170 through twoU-frames 162. Each U-frame 162 is rigidly attached to the structure ofthe cargo platform 160 and form a rotatable joint 164 at the end of eacharm 172 on the power base 170. The power base 170 controls therotational position of the arms and thus controls the height andattitude of the cargo platform 160. The ADV 100 includes one or moreprocessors to receive data, navigate a path and select the direction andspeed of the power base 170. The processors receive data from theshort-range sensors 510, 520, 530 in the cargo platform 160 and othersensors not shown in FIG. 1 .

The caster assemblies 180, 181 are mounted to the power base body 178.The caster assemblies comprise a left caster assembly 181 and a rightcaster assembly 180. Referring now to FIG. 4 , each caster assembly 180comprises a caster wheel 176, a caster frame 184, a caster pivot 186, acaster arm 188 and a mounting element 189. The caster wheel 176 isrotatably mounted in the caster frame 184. The caster frame 184 isattached to the caster arm 188 via the caster pivot 186 which allows thecaster frame 184 and caster wheel 176 pivot about the caster pivot axis192. Allowing the caster wheel 176 to pivot about the axis of the casterpivot axis 192 facilitates the wheel 176 aligning with the direction oftravel, when the caster wheel 176 is in contact with the ground.

Referring now to FIGS. 2A-2D, the power base 170 can operate in at leasttwo configurations or modes. In standard mode, depicted in FIGS. 2A-2B,the front of the clusters 175 are rotated upward to lift the front wheel174A off the ground 20. The clusters 175 comprise a driven front wheel174A and a driven back wheel 174B. The cluster 175 rotates about hub 176which connects the cluster 175 to the power base body 178. Rotating thefront of the cluster up, brings the caster wheels 176 in contact withthe ground 20 so the power base 170 and the ADV 100 rest on the backpowered wheels 175B and the caster wheels 176. In standard mode, contactwith the ground and motion of the power base 170 cause caster frame 184and wheel 176 to align with the direction of motion.

In four-wheel model, depicted in FIGS. 2C-2D, the clusters 175 arerotated to put both the front 174A and back powered wheels 174B on theground 20 and lift the caster assemblies 180, 181 off the ground. Infour-wheel mode, the caster assemblies 180, 181 are tilted back so thatthe rotation axis of the pivot 192 tilts backward from a vertical axis196. The pivot plane defined by the caster pivot axis 192 and thevertical axis 196 is parallel to the centerline of the power base. Infour-wheel mode, the backward tilt of the pivot axis 192, alignment ofthe pivot plane, and gravity also cause the caster wheel 176 align withthe centerline of the power base body 178. However, the caster frames184 and the caster wheel 176 may swing or rotate about caster pivot axis192 in response to motion of the ADV 100.

Referring now to FIGS. 3A, 3B, the swinging motion of the caster frameand wheel 184, 176 may interfere with the field of view (FOV) 512 of theforward looking sensors including sensor 510. Movement of the casterwheels within the FOV 512 of the sensors may interfere with thedetection of obstacles and surface type by obscuring part of the fieldof view or by moving unpredictably within the field of view. It isbeneficial to obstacle detection to minimize the pivoting movement ofthe caster wheels 176 and to hold the caster wheels in an orientationaligned with the centerline of the power base body 178. Aligning thecaster wheels 176 with the power base body 178 has an additional benefitof having the wheels generally pointing in the right direction when thepower base 170 transitions back to standard mode. The power base may 170wobble or move unpredictably if the casters are not approximatelyaligned with the base when the caster wheels 176 contact the ground 20as the power base transitions to standard mode.

The design position for each caster is desired rotational position ofthe caster frame about the pivot axis relative to other parts of theADV. In an example, the design position aligns the caster frame 184 andwheel 176 with the power base body 178 as shown in FIG. 3A. In anexample, the design position aligns the caster frame 184 with the centerline of the power base body 179 (FIG. 2B).

Referring now FIG. 5 , the centering mechanism 700 comprising anactuator 705, a kingpin 710 and bearings 715, 720. The centeringmechanism 700 is located in the caster pivot shell 186A. The centeringmechanism 700 acts to align the caster frame 184 and wheel 176 with thecenterline 179 (FIG. 2D) of the power base body 178. Referring again toFIG. 5 , the centering mechanism 700 acts to apply a restoring force tothe caster frame 184 when the frame pivots away from a pre-defineddesign position. In an example, the design position aligns the casterframe and wheel 184, 176 with the power base body. The kingpin 710 isfixedly mounted to the caster frame 184 and rotationally mounted to thecaster pivot shell 186A via bearings 715, 720. The kingpin 710 rotatesabout the caster pivot axis 192. The actuator 705 applies a restoringtorque to the kingpin 710 that increases as the kingpin 710, casterframe and wheel 184, 176 rotate further from the design position. In oneexample, the restoring force is zero when the caster frame 184 and wheel176 are in the design position. The restoring force reaches a maximumwhen the caster frame 184 and wheel 176 are opposite or 180 degrees fromthe design position. If the caster rotates past 180 degrees, therestoring force decreases. Thus the caster frame 184 and wheel 176 willrotate to the design position in the most direct direction rather thanretracing its path past the 180 degree position.

Referring now to FIGS. 6A-6B, the actuator 705 comprises a compressionspring 730, a follower 740, a swashshaft bearing 750, and a swashshaft760. In FIG. 6A, the elements of the actuator 705 are unsectioned. InFIG. 6B, the follower 740 is sectioned. The swashshaft 760 is mounted tothe kingpin 710, so that the swashshaft 760 turns with the caster frame184. The swashshaft 760 may be attached to the kingpin 710 by any methodthat is well known in the art including but not limited to a key,splines, a set screw, adhesive. Alternatively, the swashshaft 760 may bemechanically connected to the caster frame 184, so the swashshaft 760turns with the caster frame 184. The swashshaft 760 may be mechanicallyattached to the caster frame by any method that is well known in the artincluding but not limited to a pin, a key, splines, screws, adhesive,welding.

Referring now to FIG. 6B, the swashshaft bearing 750 is mounted on thetilted face of the swashshaft 760. The swashshaft bearing 750 contactsthe follower 740 at nub 746. The follower 740 contacts and contains oneend of the spring 730 on follower groove 744. The compression spring 730is contained by a shell groove 186B near the top of the pivot shell186A. The spring 730 applies a downward force on the follower 740 thatis transferred to the bearing 750. The bearing 750 may be bronze,oil-impregnated sintered metal, PTFE or other lubricious material thatis hard enough to not wear or deform under the load from the follower740. In one example, the bearing 750 and swashshaft 760 are a singlepiece. In another example, the bearing 750 is roller bearing where theouter race contacts the follower 740 at nub 746 and the inner racecontacts the swashshaft 760. Such a roller bearing would significantlyreduce the friction in the actuator 705 and allow the caster frame 184to freely return to design position. In addition, the low friction ofbearing 750 minimizes the spring force required to return casterframe/wheel to the design position and thereby reduce the weight of theactuator 705 and minimize undesirable torque on the casters when thecaster wheel is on the ground.

The caster frame 184 and swashshaft 760 are shown in the design positionin FIG. 6B. In the neutral position, the spring 730 applies the minimumforce on the bearing 750 as the spring 730 is at its maximum extension.In this embodiment, the follower 740 rotates about the follower pivot742 that comprise a pin that passes through a hole in the follower andmounted in the pivot shell 186A at 186C (FIG. 4 ). The actuator 705 isin the neutral position when the lowest part of the tilted bearing 750is furthest from the pin 742, which allows the follower 740 to rotateaway from the top of the pivot shell 186A.

The design position of the caster frame 184 is set by the neutralposition of the actuator 705. The swashshaft must be properly alignedwith the caster frame 184 to match the neutral position of the actuator705 with the design position of the caster frame 184. In general, theneutral position of the actuator is the position with the lowest appliedspring force. In the example pictured in FIGS. 6A, 6B, the neutralposition for the actuator 705 has the highest part of the tilted surfaceon the swashshaft 760 aligned with the follower pivot 742.

The elements of the follower 740 are more clearly shown in FIGS. 7A and7B. In this embodiment the follower 740 has an approximate ring shape.An arm 743 extends from the ring and contains the hole for the followerpivot 742. In use, the follower rotates about follower pivot 742. Thebottom of the follower 740 includes a protrusion or nub 746 thatprovides the point of contact to the swashshaft bearing 750 of FIG. 6B.

The elements of the swashshaft 750 are more clearly shown in FIGS. 8Aand 8B. In this embodiment, the swashshaft 750 comprises a round hole761 with an shaft axis 766 and swash surface or tilted surface 764. Inthe centering mechanism 700 (FIG. 6A), the king pin 710 passes throughthe round hole 761 (FIG. 8B). The tilted surface 764 is perpendicular toswash axis 768. The swash axis 768 intersects shaft axis 766 and definesan acute angle relative to the shaft axis 766. A cylindrical extension762 provides a mount for the swashshaft bearing 750 of FIG. 6B.Returning to FIG. 8B, step 763 provides a stop for the inner race of aroller bearing 750, so the outer race is free to rotate and minimizefriction between the follower 740 and the bearing 750. A keyway 767 mayprovide a rigid mount between the swashshaft 760 and the kingpin 710.

Referring now to FIGS. 9A and 9B, turning the caster frame 184 and wheel176 away from the design position, compresses the spring 730 and createsa restoring force that pushes the caster frame 184 back toward thedesign position. In FIG. 9A, the caster frame 184 and wheel 176 hasrotated more than 90 degrees from the design position. The cutaway viewof FIG. 9B, shows the swashshaft 760 has rotated with the caster frame184 so that the high point of the bearing 750 is nearly opposite thefollower pivot 742. The high point of the bearing 750 lifts up thefollower, rotating it about the follower pivot 742 and compressing thespring 730. The increased spring force will tend to push the swashshafttoward the neutral position and thereby push the caster frame backtoward the design position.

An alternative follower is show in FIGS. 10A-10C. Referring now to FIG.10A, the arrangement of the actuator 705 is unchanged. The swashshaft760 turns with the caster frame 184, which causes the tilted bearing 750to push the alternative follower 770 upward and compress the spring 730.The alternative follower 770 does not rotate about a pivot pin. Thealternative follower 770 moves axially inside the pivot shell 186A. Thespring 730 is a compression spring aligned with kingpin 710 and axiallycontained by the top of the pivot shell 186A and the follower 770.

Referring now to FIGS. 10B, 10C, the alternative follower 770 comprisesa groove 774 that contacts and radially constrains one end of the spring730. The follower surface 772 contacts the bearing 750. The swashshaft760 and the bearing 750 are in the neutral position in FIG. 10A, wherethe follower surface 772 is approximately aligned with the tiltedsurface of the bearing 750. In other examples the follower surface 772have another angles and may not be planar. The follower surface 772 willalways have a section that is axial further from the spring groove 774and another section that is axially closer to the spring groove 774. Thealternative follower 778 includes at least one anti-rotation tab 778that fits into a slot in the pivot shell 186A and prevents thealternative follower 770 from rotating about the kingpin 710. In oneexample, the follower has a second rotation tab 778 at an angle of lessthan 180 degrees from the first tab 778. The two tabs encourage thealternative follower 770 to move axially without rotating about thekingpin 710 or an axis perpendicular to the kingpin 710.

In compliance with the statute, the present teachings have beendescribed in language more or less specific as to structural andmethodical features. It is to be understood, however, that the presentteachings are not limited to the specific features shown and described,since the means herein disclosed comprise various ways of putting thepresent teachings into effect. While the present teachings have beendescribed above in terms of specific configurations, it is to beunderstood that the present teachings are not limited to these disclosedconfigurations. Many modifications and other configurations will come tomind to those skilled in the art to which these teachings pertain, andwhich are intended to be and are covered by both this disclosure and theappended claims. It is intended that the scope of the present teachingsshould be determined by proper interpretation and construction of theappended claims and their legal equivalents, as understood by those ofskill in the art relying upon the disclosure in this specification andthe attached

The invention claimed is:
 1. A caster mount on a vehicle for controllingthe rotational position of the caster comprising: a first part mountedto a base of the vehicle; a second part rotatably mounted within thefirst part, the second part rotating about a castor pivot axis andhaving a rotational position with respect to the first part, and thesecond part having a design position; and a spring actuator that appliesa force on the second part, the force increasing with an angulardifference between a rotational position and the design position of thesecond part, the spring actuator comprising: a compression springoriented along the castor pivot axis; a swashshaft attached to thesecond part, the swashshaft including a bearing surface characterized byswashshaft axis that intersects the caster pivot axis at an acute angle,the bearing surface being centered on the swashshaft axis. a follower,the follower contacting the bearing surface and the compression spring,wherein the follower, driven by the swashshaft, progressively compressesthe compression spring as the anglar difference increases.
 2. The castermount on the vehicle of claim 1, wherein the follower is rotatablyconnected to the first part via a pin, the pin being perpendicular tothe castor pivot axis.
 3. The caster mount on the vehicle of claim 1,wherein the follower is connected to the first part via a hinge, thehinge having an axis perpendicular to the castor pivot axis.
 4. Thecaster mount on the vehicle of claim 1, wherein the follower is allowedto move axially and constrained by the first part from rotating aboutthe caster pivot axis.
 5. The caster mount on the vehicle of claim 4,wherein the follower has a first surface, surface, the first surfacebeing in contact with the bearing surface, the first surface beingperpendicular to the swashshaft axis when the second part is in thedesign position.
 6. The caster mount on the vehicle of claim 1, whereinthe second part includes a kingpin, the kingpin rigidly attached to theswashshaft.
 7. The caster mount on the vehicle of claim 1, wherein thedesign position aligns the caster frame with a centerline of the vehiclebase.
 8. The caster mount on the vehicle of claim 1, wherein theswashshaft comprises a fixed portion attached to the second part and abearing portion that includes the bearing surface.
 9. The caster mounton the vehicle of claim 8, wherein the bearing portion is a rollerelement bearing with an outer race
 10. The caster mount of the vehicleof claim 9, wherein the outer race is the only part of the swashshaftthat contacts the follower.
 11. The caster mount of the vehicle of claim1, wherein the second part comprises a caster fork and a caster wheel.The caster wheel rotatably attached to the caster fork.
 12. The castermount of the vehicle of claim 1, wherein the second part is capable ofrotating fully around the caster pivot axis.
 13. The caster mount of thevehicle of claim 1, wherein the compression spring is one of a coilspring, a flat spring and a bulk material spring.